Power-over-Ethernet (PoE) is a standard enabling the powering of devices requiring moderate power consumption by means of a standard Ethernet cable, e.g. a Cat5 or Cat5e type of cable. Typically, in a Power-over-Ethernet System, a number of devices are attached to one or more of such cables, whereby the devices are powered by the cable via PoE switches. Such PoE switch (or in general, a PoE device) is generally applied as a node in a star type network topology and serves to direct the network traffic between the different Ethernet branches of the network. Such a PoE switch equally provides electrical energy according to the PoE-standard to the connected devices. Such devices can e.g. include lighting applications for domestic or professional lighting or may be sensors or the like.
Such a set-up has been proven a practical method to provide electrical energy to a plurality of connected devices, up to a distance of 100 m. Such a system has also proven to be suited if the power of the connected devices is low, or the distance is short, and if the powered devices are supposed to operate in continuous running mode, e.g. routers, DSL modems, other switches, and the like.
At present, it becomes clear that also other devices than those for computer and network technology, e.g. light sources, could be favorably supplied with energy by this method. Such a configuration could e.g. comprise a number of detached PoE-devices or PoE-switches, whereby each device or switch powers a number of devices in its close proximity, e.g. light sources. Characteristics for such devices are a comparatively high power requirement, they are operated intermittently, and often do not need persistent network connection.
In order to provide power to the connected devices and in order to provide in its own power requirement (e.g. to power a control unit controlling the operating of the switch), the PoE switches are provided with an own PoE power supply locally such as a mains supply connection. In general, such a PoE switch acquires its power supply from the local PoE power supply, irrespective of whether or not a device that is connected to the switch is operated or requires power. As such, an important power consumption (also referred to as standby power) can be noticed when the PoE switch is not powering a connected device. In view of the fact that PoE Systems are typically used for comparatively low or moderate power applications, the standby power requirements of the PoE switches as generally applied may adversely affect the overall efficiency of the PoE system.
It has been proposed to mitigate the standby power by providing a dedicated low power supply for this purpose in the PoE switch, providing power to the switches own functions in case of no attached devices require a PoE-supply; this may however result in a noticeable increase of the cost price of the system.